Coiled-Coil Hydrogels: Effect of Grafted Copolymer Composition and Cyclization on Gelation

• Published in: Macromolecules 2009-03, Vol.42 (6), p.2265-2274
• Main Authors: Dušek, Karel, Dušková-Smrčková, Miroslava, Yang, Jiyuan, Kopeček, Jindřich
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Solution and gel properties
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma801906j

A mean-field theoretical approach was developed to model gelation of solutions of hydrophilic polymers with grafted peptide motifs capable of forming associates of coiled-coil type. The model addresses the competition between associates engaged in branching and cyclization. It results in relative concentrations of intra- and intermolecular associates dependent on associate strength and motif concentration. The cyclization probability is derived from the model of equivalent Gaussian chain and takes into account all possible paths connecting the interacting motifs. Examination of the association−dissociation equilibria, controlled by the equilibrium constant for association taken as input information, determines the fractions of inter- and intramolecularly associated motifs. The gelation model is based on the statistical theory of branching processes, and in combination with the cyclization model, it predicts the critical concentration delimiting the regions of gelled and liquid states of the system. A comparison between predictions of the model and experimental data available for aqueous solutions of poly[N-(2-hydroxypropyl)methacrylamide] grafted with oppositely charged pentaheptad peptides, CCE and CCK, indicates that the association constant of grafted motifs is four orders of magnitude lower than that of free motifs. It is predicted that at the critical concentration of each motif of about 6 × 10−7 mol/cm3, about half of the motifs in the associated state are engaged in intramolecular bonds.